EtherChannel Consistency: Repair a Mode Mismatch

Bundle lab · $29.99

Advanced CCNP troubleshooting lab: a pair of Layer-2 switches are connected by a two-link EtherChannel intended to carry VLAN 90 between access hosts. The starter configuration ships broken on purpose: the inter-switch bundle won’t form due to incompatible aggregation modes, and a trunk allow-list drift on one side prunes VLAN 90. Diagnose with IOS show commands, correct the EtherChannel mode so LACP forms the Port-channel, and restore trunk policy so same-VLAN hosts can communicate.

Learning objectives

• Identify EtherChannel bundling failures using show etherchannel summary and show etherchannel detail.
• Determine and correct an aggregation mode incompatibility so both member links bundle via LACP.
• Validate and fix trunk policy so the required VLAN is transported end-to-end.
• Confirm same-VLAN host reachability and interpret LACP neighbor and bundle flags.

Troubleshooting focus

• Correlate member interface states and flags (suspended/standalone vs bundled) with the Port-channel state.
• Compare EtherChannel protocol and mode on both ends; incompatible pairs will not bundle.
• Inspect trunk mode, native VLAN, and allowed VLAN lists on the Port-channel to ensure the intended VLAN is transported.
• Use host-to-host pings in the user VLAN to confirm forwarding after each fix.